The present invention relates generally to plasma cutting systems and, more particularly, to a system for receiving welding power from a welding device and converting the welding power to plasma-cutting power. A converter circuit is configured to receive the welding power and automatically adjust current and voltage levels, and invert polarity of the power to deliver plasma-cutting power to effectuate a plasma cutting process.
Plasma cutting is a process in which an electric arc is used for cutting a workpiece. Plasma cutters typically include a power source, an air supply, and a torch. The torch, or plasma torch, is used to create and maintain the plasma arc that performs the cutting. A plasma cutting power source is typically included to receive input power from one of two sources. Specifically, the plasma cutting power source is configured to receive alternating current (AC) power from either a transmission power receptacle or a generator. The plasma cutting power source conditions and converts the AC power to direct current (DC) output power appropriate for generating the plasma cutting arc and performing the desired plasma-cutting process.
However, plasma cutting operations are often desired at remote locations where neither a transmission power receptacle nor a generator is available. While these traditional AC power sources may not be available at such remote locations, welding systems having integrated engine-driven generators, or engine-driven welders, are often present at these remote locations because such field environments frequently require both plasma cutting and welding operations. While it would be desirable to utilize the generator integrated in an engine driven welder as a source of power for performing plasma-cutting processes, such has been precluded for a variety of reasons.
First, traditional plasma cutting systems are typically designed to receive AC power from either a transmission power receptacle or a generator. Accordingly, traditional plasma cutting systems are designed to convert AC power conforming to strict standards, for example 120 Volts (V), 60 Hz power, to plasma cutting power. While some engine-driven welders include auxiliary power receptacles for supplying 120V, 60 Hz power to power devices such as power tools and lights, these engine-driven welders typically have an output power capacity of less than 3 kilowatts (kW). As such, the power output capacity of these auxiliary outputs is insufficient to power plasma-cutting processes. That is, while these auxiliary outputs of engine-driven welders are designed to provide sufficient AC power, for example, 230 VAC to operate devices such as handheld power tools and lights, the power input requirements of plasma cutters typically surpass the output capabilities of these auxiliary outputs of engine-driven welders.
Second, while more substantial power outputs are typically available via the welding output of engine-driven welders, plasma cutting systems are designed to receive AC power conforming to specific constraints and cannot generally operate from DC welding power. That is, the power delivered from engine-driven welders to effectuate welding procedures is typically DC power that has been specifically conditioned to perform a desired welding process, for example 80 VDC. Therefore, traditional plasma cutters are incapable of utilizing the power delivered by engine-driven welders to the welding output.
Third, beyond typically being incapable of utilizing the type of power supplied to the welding output because the power is DC rather than AC, there are often additional impediments to utilizing power from the welding output to drive a plasma cutter. For example, welding processes such as stick welding typically require that the electrode of the welding torch be positively charged. On the other hand, plasma cutters generally require that the electrode be negatively charged. Therefore, not only is the power supplied via the welding output of the engine-driven welder inadequate for plasma-cutting, the polarity of welding power is reversed with respect to that required by the plasma cutter.
Accordingly, some plasma cutters have been developed to receive power from a welding output of an engine-driven welder. These systems utilize silicon controller rectifiers (SCRs) to perform the switching required to convert the welding power delivered by the engine-driven welder into power acceptable for plasma cutting.
However, though overcoming some of the drawbacks identified above, these plasma cutting systems having SCR-based power converters did not reverse the polarity of the power supplied by welding power source. As such, since welding operations often require that the welding electrode have a positive polarity, the operator must manually adjust the system to provide the plasma cutting electrode with a negative charge.
Furthermore, these systems typically require a rectified three-phase power supply to properly create the plasma cutting power. That is, when supplied with rectified single-phase power, these plasma cutters having SCR-based power converters are generally not capable of properly converting the rectified single-phase welding power to plasma cutting power. However, three-phase engine-driven welding power sources are typically significantly less common in the welding industry, which considerably reduces the compatibility of the plasma cutter with available engine-driven welders.
Also, these systems lack controls to stop the engine drive of the engine-driven welder from being overpowered and causing engine speed to fall. Therefore, it is possible for an operator to inadvertently draw more power than the engine-driven welder is capable of providing. As such, the engine is overpowered and speed drops. Correspondingly, the power delivered by the engine-driven welder drops and can continue to drop until the engine fails.
It would therefore be desirable to design a plasma cutting system that is capable of receiving rectified single-phase welding power and accurately converting the rectified single-phase welding power to plasma cutting power. Furthermore, it would be desirable to design a plasma cutting system capable of receiving DC welding power from an engine-driven welder, and having a DC to DC converter and control system capable of processing the received DC welding power and converting it to power necessary for generating a plasma cutting arc without overpowering the engine-driven welder. Additionally, the DC to DC converter should be configured to automatically invert the welding power voltage polarity for a desired plasma-cutting process. Also, it would be desirable that the DC to DC converter not adversely affect the size and portability of the plasma cutter.